Murray is currently preparing for his third-round match against Ricardas Berankis at the Australian Open, which takes place on Saturday.

But the British No. 1 was forced to answer questions on the claims of Rochus, a retired Belgian player, who claimed the game's top players are playing at a standard not achievable by natural means. "The guys can't play five or six hours and then come back the next day and run around like a rabbit," Rochus was quoted as saying.

Murray was beaten by Novak Djokovic in a semi-final that lasted almost five hours at last year's Melbourne tournament, and then the Serb returned to defeat Rafael Nadal in six hours two days later. Murray insists the top players are able to match such demands due to the hard work they put in during training.

"I would say that is far from the truth," Murray said of Rochus' claim. "Anyone can see the amount of hours of training and practice that go into what we do and there are other sports that are far more challenging than tennis endurance-wise. When guys play five or six hours in the slams, like we often do, we have a day's rest.

"I was told that on his day off after our match here last year Novak didn't practice, didn't hit a ball, didn't get out of bed until three o'clock. Providing you put the work in it doesn't mean it hurts any less when you have to play a couple of days later after a five-hour match but I would not say it's impossible."

Murray also credited Nadal with raising the physical level of tennis, saying: "Rafa was the first one to have that physique that looked like a true world-class athlete across any sport. Tennis players are always in good shape, but I think he looked like he could do any sport. The game has changed for sure physically. It's much more demanding and I've adapted my preparation and training."

Djokovic admitted on Friday he has not had a blood test in over six months, but expressed his confidence that anti-doping measures are sufficient to prevent a Lance Armstrong scenario happening in tennis.

"I wasn't tested with blood for the last six, seven months," he said. "It was more regular in the last two, three years. I don't know the reason why they stopped it.

"As long as it's fair, it's clean, we're trying to protect the identity of this sport. I believe tennis players are [some] of the cleanest athletes in the world and one of the most competitive sports. So as long as we keep it that way, I have no complaints about testing."